The present invention relates to a structure suitable for mounting an antenna base to a vehicle body having a curved surface.
As shown in Japanese Patent Publication Nos. 8-335824A and 8-237014A, in a conventional attaching structure for mounting an antenna to a vehicle body, a single fixing screw is arranged so as to protrude downward from an antenna base. Then, the fixing screw is inserted into a hole drilled in a vehicle body, while a nut is engaged from the back side. Thus, the vehicle body is clamped between the antenna base and the nut, so that the antenna base is fixed to the vehicle body.
The above-mentioned conventional structure does not have a specific problem as long as the size of the antenna base is not very large and a single fixing screw suffices for fixing the antenna base reliably. However, popularization of car-installed communication equipments with composite construction in recent years leads to, in turn, necessity of the suitable antenna with composite construction, and hence increase of the size of the antenna base for mounting the antenna to the vehicle body is unavoidable. In this case, fixing the antenna base with a single fixing screw may be unstable in view of mechanical intensity. Thus, plural fixing screws are necessary for reliably fixing the antenna base to the vehicle body.
FIG. 13 shows such a structure in which two fixing screws 16 are integrally arranged so as to protrude downward in an antenna base 12 having a relatively large size. In this structure, the two fixing screws 16 integrally provided with the antenna base 12 are inserted into holes 22 drilled in a vehicle body 20, while nuts 32 are engaged with the fixing screws 16 respectively from the back side. Further, a pad 26 having elasticity is inserted between the antenna base 12 and the vehicle body 20. Thus, when the nuts 32 are tightened, the antenna base 12 is reliably fixed to the vehicle body 20, while the pad 26 prevents rain water from entering into the vehicle body through the holes 22. Here, in FIG. 13, numeral 10 indicates an antenna case in a bottom face part of which the antenna base 12 is arranged appropriately. Numeral 14 indicates a rod-shaped antenna element a pedestal end of which is fixed to the antenna case 10. Numeral 28 indicates a washer inserted between the vehicle body 20 and the nut 32.
In recent years, the vehicle body 20 is formed with a combination of complicated curved surfaces for the purpose of good appearance. Thus, there will be no problem, if the bottom surface of the antenna base 12 had a shape corresponding to the curved surface of the attached portion of the vehicle body 20. However, when the bottom surface of the antenna base 12 would not agree with the shape of the vehicle body 20, the tightening of the nuts 32 could generate deformation in the vehicle body 20 so as to follow the shape of the bottom surface of the antenna base 12.
Here, it should be noted that even in the conventional structure where a single fixing screw is arranged and protruded and where the bottom surface of the antenna base is a curved surface in agreement with the curved surface of the vehicle body, the tightening of the nut could similarly generate deformation in the vehicle body if the antenna base would deviate from an appropriate attached portion, so that the bottom surface of the antenna base would not agree with the curved surface of the vehicle body.